The present disclosure relates to a method of treating lost circulation issues stemming from loss zones during the drilling and cementing process through the use of a thixotropic cement.
Lost circulation is a well-known industry problem that may result in non-productive time during drilling and cementing and/or the loss of drilling and cementing fluids to the surrounding formation. Lost circulation is the partial or complete loss of drilling fluid or cement slurries into formation voids during drilling, circulation, running casing or cementing operations. Estimates show that these types of losses occur during drilling on approximately 20-25% of wells worldwide. Such losses can be extremely expensive and troublesome, resulting in lost rig time, stuck pipe, blow-outs and sometimes the outright abandonment of expensive wells. These losses also cause reduced production and lost man-hours among other things.
Lost circulation problems can happen at any depth and can occur when the total pressure exerted against the formation exceeds the formation breakdown pressure or when there are sizeable fractures or fissures connecting the wellbore to the surrounding formation. Lost circulation problems are generally caused by four types of formations: 1) natural or induced fractured formations; 2) vugular or cavernous formations; 3) highly permeable formations; and 4) unconsolidated formations. These formations can be aggravated upon drilling or due to severe loads applied during drilling on weak formations having a low fracture gradient. These formations can cause many levels of losses depending on their size and location.
One method of addressing lost circulation is to add sized particulate matter to the fluid being placed into the formation with the expectation that properly sized particulates will then block fissures, pore face, or other openings for the wellbore to the surrounding formation. However, such particulate solutions are best suited for wellbores in locations where relatively minor losses are seen. Wellbores experiencing moderate to severe losses are less emendable to a sized particulate solution. Furthermore, losses that are treated during drilling can sometimes resume during cementing due when, for example, a cement with higher density than drilling fluid is used.
The usual procedure to treat moderate to severe losses during drilling is to pump a batch of lost circulation material (LCM) fluid, often called an LCM pill. This pill fills the crevices of the loss zone and may also provide wellbore strengthening to enable further drilling. However, in case of severe losses, even such a pill treatment may not be effective. In such cases, chemical solutions like polymers, viscofiers, foams, polyurethanes, calcium carbonates and crosslinked gels have been suggested. However, such chemical solutions may be inconsistent to apply and tend to vary based on the well temperature. Moreover, they can be difficult to place, requiring expertise to ensure that the correct area surrounding the wellbore is treated. There is a need for a methodology with a greater degree of success and consistency in treating loss zones.